In motor vehicles having an internal combustion engine, the fuel is conveyed from a fuel tank with the aid of a fuel pump, and is supplied to the fuel injection valves, also called injectors, via fuel lines. Excess fuel standardly flows back to the fuel tank via a return line. In internal combustion engines having high-pressure injection, in particular in internal combustion engines having self-ignition, an additional pump is connected to the fuel pump that produces a very high pressure in a high-pressure area, also called a rail, that is connected to the injectors. In such fuel supply systems, there is the danger of a leak in the high-pressure part, so that fuel flows into the return line. This is standardly called an internal leak. In addition, leakage to the outside is possible, in which the fuel flows into the engine compartment under high pressure. Increased leakage of an injector results in a lasting decrease in the rail pressure. This can result in a defect of the internal combustion engine.
German Patent Publication No. DE 197 03 891, a method and a device are known for recognizing a leak in a fuel supply system of an internal combustion engine, in particular an internal combustion engine having a common-rail system, in which a pressure sensor acquires the pressure in the high-pressure area. Here, at least two pressure values are acquired at different times, and from these two pressure values a fuel quantity balance is determined, and the presence of a fault is inferred on the basis of the fuel quantity balance. While such a method and such a device can recognize a leak in a general fashion, it is however not possible to recognize a cylinder-specific leak in this way. In the case of a leak, it is thus necessary to exchange all the injectors, even if for example only one injector has a leak. This is disadvantageous not only from the point of view of cost, but also because the exchange of all the injectors requires considerable assembly work.
In addition, for workshop purposes only, an individual-injector-specific leak measurement is known that uses a measurement tube at the injector; however, this is used only for passenger vehicles, and in addition is not accepted by all vehicle manufacturers, because the leakage measurement requires open handling of fuel while the internal combustion engine is running, which presents a significant safety risk.
The present invention is therefore based on the object of disclosing a method and a device for checking for leaks in a fuel injection valve of an internal combustion engine, by which it is possible to determine in a simple and reliable manner whether an individual injector has a leak.